<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Element 对象</title>
</head>
<body>

<a>点击</a>
<input id="btn_set" type="button" value="设置属性">
<input id="btn_remove" type="button" value="删除属性">

<script>

  // 获取 btn
  var btn_set = document.getElementById("btn_set");
  btn_set.onclick = function() {
    // 获取 a 标签
    var element_a = document.getElementsByTagName("a")[0];
    element_a.setAttribute("href", "https://www.baidu.com");
  }

  var btn_remove = document.getElementById("btn_remove");
  btn_remove.onclick = function() {
    // 获取 a 标签
    var element_a = document.getElementsByTagName("a")[0];
    element_a.removeAttribute("href");
  }



</script>

</body>
</html>